make it easier to determine what is a "bad" DCLS value

[souders]

I implemented the DCLS code provided here and tried it on a few pages. I got values that ranged from 0.5 to 1.5. My initial reaction was wondering what was a good score and what was a bad score. It sounds like DCLS could get very large - in the thousands potentially.

I think it would be better if the score could be on a fixed scale - say 0 to 100. This would let people have a better understanding of whether layout instability was a priority issue. Since it's not a time-based metric, it might be better to invert it so a score of 100 is perfect (like Lighthouse).

(I read the previous discussion about measuring Layout INstability vs Layout STability. Sorry if this rehashes that debate.)

[skobes-chromium]

Having an upper bound is a good idea. We actually do limit the CLS score to 10.0 when we report it to UKM (data source for the Chrome User Experience Report). We could impose a similar limit for the Web Perf API. Differentiating beyond 10.0 is probably not useful.

[mmocny]

I believe we can now close this, since we have published guidelines on Good, Needs Improvement, and Bad CLS scores.

[npm1]

I think we could add an example with a diagram showing ~half the viewport shifting and explaining what the score would be in that case.